Insulating materials



Jan. 20, 1953 H THURNAUER ET AL 2,625,220

INSULATING MATERIALS Filed May 20, 1947 FIG. 1

DIELECTRIC CONSTANT I0 5O 6O 7O 8O 9O PERCENTAGE TIO (by weight) BuTiO-TiO mixture I FIG. 2

CAPACITY DRIFT mmf/ mmf/ "cxlo"+ 0 IO 20 3O 40 50,60 8O 9O PERCENTAGE ao(b weight) [30110 -1109 mixture In v e h to rs: Hans Thumauer JamesDeaden'clr their Attorney Patented Jan. 20, 1953 UNITED- STATES ?ATENTOFFICE INSULATING MATERIALS Hans Thurnauer, Chattanooga, and JamesDeaderick, Signal Mountain, Tenn.

Appiication May 20, 1947, seriairi 749,339

(Cl. ce-39) 5 Claims.

This invention relates to ceramic insulating materials having highdielectric constants and desirable coeflicients of capacit and is acontinuation-in-part of our application, Serial No. 413,340, filedOctober 2, 1941, and issued as Patent No. 2,429,588 of October 21, 1947.

Ceramic materials containing titanium dioxide as one of their chiefingredients are known to have unusually high dielectric constants.Whereas other ceramic materials, such as porcelain, steatite, lava,glasses, etc., have dielectric constants between 5 and 8, ceramicmaterials containing a high percentage of titanium dioxide havedielectric constants between is and 112. There are in commercial useceramic materials to be used as dielectrics in electric condensers whichnot only have high dielectric constants but also have definedtemperature coefficients of capacity. Such condensers are used asbalancing or compensatin units in oscillating circuits to compensate forcapacitance and inductance changes due to temperature variations ofclimate or heating of the oscillating circuit during operation. Suchcondensers have dielectric constants between 6 and 110 and temperaturecoefficients of capacity between plus 1.2 X 10- mmf./mmf./C. to minus'7.5 10 mmf./mmf./C., mmf. as here used meaning micro-micro-farad.

The positive temperature coefiicient of capacity usually is connectedwith the lower dielectric constant (e. g. 6) and the highest negativetemperature coefficient of capacity with the highest dielectric constant(e. g. 110). A material with zero temperature coefficient of capacityusually has a dielectric constant between 1'? and 19.

It is, of course, highly desirable to employ as dielectrics incondensers materials having the highest possible dielectric constants inorder to obtain condenser units of minimum physical dimensions anddielectric capacities as high as possible.

We have now been able to prepare ceramic electric insulating materials,etc., which have exceptionally high dielectric constants and temperaturecoefficients of capacity within well defined limits.

Our invention is based on the discovery of the unusual and unexpectedlectric insulating characteristics of barium titanate, and of bariumtitanate when admixed with varying proportions of titanium dioxide.Depending upon the final properties, as to dielectric constant andtemperature coefiicient of capacity desired, the proportion of bariumtitanate and titanium dioxide can be varied between 100 parts of bariumtitanate and 0 part of titanium dioxide and 10 parts of bariumtitanateand 9Q parts of titanium dioxide, with a constant amount of additionalfluxes, as is customary in this art, added to. each mixture. In thepractice of our inventionw can use pure barium titanate, BaTiOs, or wecan use commercial barium titanate which has a typical analysis asfollows: TiOz 34.3%, BaO 63.9%, F9203 133%, other oxides 1.77%.

We. shall now describe ways by which our invention can be practiced.

Finely divided barium titanate, finely divided titanium dioxide andfinely divided fluxes are carefully mixed, either. dry or wet, to form ahomogeneous mixture. We prefer the mixture to be of such fineness as topass a 325 mesh sieve, but this is a matter of choice. If thernixturehas been prepared wet, it is carefully dri d, then organic binders, suchas wheat flour, dextrine, etc., are added, as usual in this art, tofacilitate subsequent forming. The prepared ceramic body is then shapedaccording to Well-known ceramic methods, such as compression pressing,extrusion, etc. In cases where a certain amount of plasticity is desiredto form complicated shapes, moisture may be added to the powder toimprove its plastic properties.

After forming, the shaped pieces are fired in ceramic kilns in oxidizingor inert atmosphere to prevent the formation of any lower oxide forms oftitanium, other than TiOz. The firing temperature has to be such thatthe pieces are fired to full vitrification so that their moistureabsorption is less than 0.1%. The temperature of firing has been foundto be ordinarily between 1200 C. and 14:00 O. For the maintenance of aninert atmosphere, we prefer the use of electrically fired kilns, but donot exclude kilns fired with other kinds of fuel.

The vitrified ceramic materials manufactured by the above-mentionedmethod are mechanically strong, have high dielectric strength, lowdielectric loss factor at high frequency and are especially suitable asdielectric media in condensers or capacitors. Any of the ceramicmaterials in the series barium titanate-titanium dioxide may be usefulas a dielectric in a ceramic condenser, depending on the temperaturecoefiicient of capacity or the dielectric constant of the assembled unitdesired, but of special interest is the follow ing composition:

This composition has been found to have the extremely high dielectricconstant of 1200 (approximately twelve times higher than titanium 3dioxide), a temperature coefiicient of capacity between 40 C. and 80 C.of plus 12 10' mmf./mmf./C., and a power factor of 1.0%.

In the above example any of the common fluxes can be used in place ofthe calcium phosphate, and we make no claim to the use of such fluxesgenerally. In the preparation of ceramic insulating materials it iscustomary to mix the insulating material with a suitable flux before thematerial is fired. Likewise, the use of organic binders before firing isconventional.

We have prepared a whole series of barium titanate-titanium dioxidedielectrics, varying in proportions from 100% BaTiOa to of BaTiOs and 90of TiOz. So that those skilled in the art may be appraised of theelectric characteristics of such mixtures, we have shown, on theappended single sheet of drawings, two graphs covering the systemBaTiOs-TiOz. Figure I shows the variation in dielectric constant, andFigure II shows the variation in capacity drift.

We are aware that magnesium titanate has been used as a dielectricmaterial, as in the patent to Alberts-Schonberg 2,165,819, and make noclaim thereto. Magnesium titanate has a dielectric constant of to 18whereas barium titanate has a dielectric constant of about 1200. Otherimportant differences exist between the two substances, but the highdielectric constant of barium titanate is outstanding.

Having described our invention, we claim:

1. A ceramic insulator comprising a vitrified body formed from a mixturehaving a dielectric composition of 55 to 100% barium titanate and up to45% titanium dioxide.

2. A ceramic insulator comprising a vitrified body formed from a mixturehaving a dielectric composition of 68 to 100% barium titanate and up to32% titanium dioxide, said material having a dielectric constant between100 and 1200.

3. A ceramic insulator comprising a vitrified body having a dielectricconsisting of barium titanate and a dielectric constant of approximately1200.

4. A ceramic insulator comprising a vitrified body having a dielectriccomposed of barium titanate and up to titanium dioxide, said body havinga dielectric constant of between 32 and 1200.

5. A ceramic insulator comprising a vitrified body having a dielectircconsisting of barium titanate.

HANS THURNAUER. JAMES DEADERICK.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,165,819 Alberts-Schonberg July11, 1939 2,218,655 Peterson Oct. 22, 1940 2,220,765 Hirose et a1. Nov.5, 1940 2,277,733 Wainer et a1 Mar. 31, 1942 2,277,734 Wainer et al Mar.31, 1942 2,429,588 Thurnauer et al. Oct. 31,1942

FOREIGN PATENTS Number Country Date France 1931

1. A CERAMIC INSULATOR COMPRISING A VITRIFIED BODY FORMED FROM A MIXTUREHAVING A DIELECTRIC COMPOSITION OF 55 TO 100% BARIUM TITANATE AND UP TO45% TITANIUM DIOXIDE.
 5. A CERAMIC INSULATOR COMPRISING A VITRIFIED BODYHAVING A DIELECTRIC CONSISTING OF BARIUM TITANATE.